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From: Thomas Gleixner <tglx@linutronix.de>
To: Michael Bohan <mbohan@codeaurora.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	linux-arm-msm@vger.kernel.org,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/2] hrtimer: Consider preemption when migrating hrtimer cpu_bases
Date: Thu, 18 Apr 2013 11:40:32 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LFD.2.02.1304181138290.21884@ionos> (raw)
In-Reply-To: <1365628068-32738-2-git-send-email-mbohan@codeaurora.org>

On Wed, 10 Apr 2013, Michael Bohan wrote:

> When switching to a new cpu_base in switch_hrtimer_base(), we
> briefly enable preemption by unlocking the cpu_base lock in two
> places. During this interval it's possible for the running thread
> to be swapped to a different CPU.
> 
> Consider the following example:
> 
> CPU #0                                 CPU #1
> ----                                   ----
> hrtimer_start()                        ...
>  lock_hrtimer_base()
>  switch_hrtimer_base()
>   this_cpu = 0;
>   target_cpu_base = 0;
>   raw_spin_unlock(&cpu_base->lock)
> <migrate to CPU 1>

Errm. switch_hrtimer_base() is called with interrupts disabled and
they stay disabled, so how exactly is the task going to be migrated?

Thanks,

	tglx

  reply	other threads:[~2013-04-18  9:40 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-10 21:07 [PATCH 0/2] hrtimer preemption bug fixes Michael Bohan
2013-04-10 21:07 ` [PATCH 1/2] hrtimer: Consider preemption when migrating hrtimer cpu_bases Michael Bohan
2013-04-18  9:40   ` Thomas Gleixner [this message]
2013-04-19  1:37     ` Michael Bohan
2013-04-10 21:07 ` [PATCH 2/2] hrtimer: Prevent enqueue of hrtimer on dead CPU Michael Bohan
2013-04-18  9:44   ` Thomas Gleixner

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